1. Field of the Invention
The present invention relates generally to radio frequency (RF) controlled alarm systems, and particularly to a remote controlled alarm system for assisting in the recovery of a stray person or pet by a guardian.
2. Discussion of the Known Art
We hear all too often about the tragic loss of children who are abducted during just those few moments while a parent or guardian's attention was diverted in a crowded department store, amusement park or shopping mall. Even though the abducted child may be near enough to its parent to call for help, or may be led past others who could be of help to reunite the child with its parent, the child may understandably be afraid to call for help for fear of being harmed by the abductor.
Certain services have been made available to the public as an aid in locating and recovering lost children. Advertising post cards are widely distributed through the U.S. Mail having a merchant's advertisement on one side of the card and photographs of one or more missing children with vital statistics and an "800" phone number printed on the other side, in case the recipient recognizes the lost child and wants to report the child's whereabouts.
Community programs have been introduced through the public elementary schools. For example, a local police department may send personnel to a school over the weekend with finger printing kits. The community is invited to have their children's fingerprints taken and the parents are given the fingerprints to take home for safe keeping. Such a program, sometimes called "Kinder Prints", is viewed as a means for protection against child abduction but in fact serves only to provide a positive means of child identification after an abduction takes place. It is of course preferable to take precautions before an abduction may occur and try to negate the possibility that an abduction will occur in the first instance.
Simple mechanical arrangements are also known by which a young child can be kept within a certain distance of a parent or guardian. A tether or child "leash" arrangement by which an adult holds one end of a long strap connected at its other end to a harness worn by the child, is an example of a known device for ensuring that a child does not stray far and get into trouble without the parent's knowledge.
Various monitoring systems are also known which use RF transmitters and receivers for enabling a parent to monitor the whereabouts of a child without the need for a mechanical connecting device. For example, U.S. Pat. No. 4,899,135 (Feb. 6, 1990) shows a child monitoring device comprised of a transmitting unit carried by the child, and a receiving unit carried by the child's guardian. The purpose of the device is to alert the guardian once the child strays beyond a certain distance, is abducted or falls into water. The child's unit is carried in a holster and emits a constant signal which is received and detected by the guardian's unit. A loss of the received signal at the guardian's unit initiates an audible warning signal. At such time, closing a switch on the guardian's unit causes a signal from the latter to energize an audio tone transmitter in the child's unit.
The monitoring system of the '135 patent has certain disadvantages. First, the guardian's unit will emit a sonic warning signal only when the child strays beyond a certain distance at which a threshold receiving circuit in the unit senses that the constant signal from the child's unit has fallen below a certain signal strength. Since most parents would not want a child monitoring device to sound an alarm if the child is only two or three feet away playing within view, the threshold circuit in the guardian's unit would likely be set to cause an alarm only if the child wanders more than, say, 100 feet. But a parent or guardian would want an alarm to sound if the child is suddenly no longer in view even though he or she may be hiding only a few feet away. For example, in a department store setting with much merchandise on the floor, a child need not stray very far distance-wise so as to be no longer in view of its parent. Once the parent realizes the child is "missing", he or she may begin to shout the child's name. The child, upon hearing its parents initial shouts usually feels that its parents are angry, and will hide on purpose nearby (behind a clothes rack is common). A parent who has experienced this situation and the accompanying fright and anxiety will know that every minute a child is apparently missing seems like an eternity. Moreover, the transmission of a constant, uninterrupted RF monitoring signal from the child's unit may not be permitted under the applicable rules of the Federal Communications Commission as discussed later below.
U.S. Pat. No. 4,777,478 (Oct. 11, 1988) describes apparatus for monitoring persons in which a periodic signal is transmitted from a monitored unit (B) to a monitoring unit (C) until certain threshold conditions are exceeded. Like the arrangement of the '135 patent, the apparatus of the '478 patent is a monitoring system relying basically on the receipt by monitoring unit C of a signal transmitted from the monitored unit B, the latter being worn by a person whose whereabouts are of interest to the one holding the monitoring unit C. In the apparatus of the '478 patent, if the signal received by monitoring unit C falls below a certain threshold value, the unit then sends a signal to monitored unit B causing the latter to radiate a continuous RF signal. No audible or visual alarm is produced at the site of the monitored unit B, however.
U.S. Pat. Nos. 4,314,240 (Feb. 2, 1982) and 4,850,031 (Jul. 18, 1989) relate to devices for locating avalanche victims and also depend on a signal transmitted from a unit held by the victim to a receiver unit carried by a rescuer.
A child protector device for warning a parent that a stationary child is being abducted by sounding an alarm, is disclosed in U.S. Pat. No. 4,888,580 (Dec. 19, 1989). Basically, the device comprises a housing that contains a battery power supply, an alarm buzzer, and a magnetic switch. The housing may be hidden in a stuffed animal placed next to the child. An outside string is connected between a magnet and a strap that encircles the child's ankle. As long as the magnet is held in place on the housing, the magnetic switch is kept open and the buzzer alarm remains silent. If the child is moved by a would-be abductor so as to cause the string to pull the magnet away from the housing, the magnetic switch closes and the alarm sounds.
A remotely controlled alarm system for a stolen briefcase is known from U.S. Pat. No. 4,804,943. There, a briefcase is provided with a receiver and a siren alarm. If the briefcase is stolen, the owner operates a transmitter which signals the receiver inside the briefcase. The siren then sounds and the briefcase drops away from its handle to be retrieved by the owner, according to the patent.
Any RF based alarm system must of course comply with the applicable rules and regulations imposed by the Federal Communications Commission (FCC). Consumer devices such as garage door openers that emit radio signals periodically are permitted without a license being necessary for the operator of the device. Pertinent rules and regulations are set out by the FCC at 47 C.F.R. .sctn..sctn. 15.1, et seq. Part 15 and all other relevant sections of the FCC rules and regulations are fully incorporated by reference herein.
Specifically, 47 C.F.R. .sctn. 15.231 allows for periodic operation of a manually operated transmitter or intentional radiator in the frequency band of 40.66-40.70 MHz and above 70 MHz, provided specified field strengths and transmission time periods are adhered to. This section also encourages the use of recognition codes for identifying a receiver or sensor that is to be activated. 47 C.F.R. .sctn. 15.205 and .sctn.15.209 place further restrictions on the transmitter signal frequency and signal strength. In any event, it is contemplated that an alarm signal transmitter such as the one disclosed below and capable of sending a detectable signal of sufficient strength up to a range of about one-quarter mile, can be constructed with a suitable antenna (see 47 C.F.R. .sctn. 15.203) in compliance with the relevant FCC rules and regulations.